Anegada ground iguana description

The Anegada ground iguana was once distributed over the entire Puerto Rico Bank but, as its common name implies, its natural range is now restricted to the island of Anegada in the British Virgin Islands (4). This relatively large, stout species of Cyclura has a dusty-brown coloured back and a buff-white to pale grey belly. By contrast, the legs, sides, tail base and dorsal spines are strikingly coloured with varying amounts of brilliant turquoise blue, particularly pronounced in males (2)(4). Juveniles have a grey to moss-green back and sides and are distinctively patterned with a series of wide grey to black forward-pointing chevrons, which fade and are generally lost as the individual matures (2)(4). Eyes are normally a dull yellow, but flush bright crimson when the iguana becomes agitated (2)(4).

Related species

Anegada ground iguana biology

The release of livestock on Anegada in 1968 has not only caused a decline in population numbers, but has also had a profound affect on the Anegada ground iguana’s social organisation and diet (2). Estimates in the late 1960s showed the average home range size for iguanas on Anegada to be small, at less than 0.1 hectares, and non-overlapping (2)(4). Additionally, there were roughly equal numbers of males and females, each individual was found to occupy one principle burrow, and habits indicated monogamy, with pairs inhabiting separate but proximate burrows in a joint home range isolated from other pairs. However, by 1991, the sex ratio had changed to two males to every female. Now, home ranges are quite large and overlap, at 6.6 hectares for males and 4.2 hectares for females; with these changes thought to be a result of male competition for far more limited females (4). Males suspected of having a mate have noticeably smaller home ranges, presumed to be due to their greater need to guard the female against wandering bachelors. Females typically lay one clutch of around 12 to 16 eggs per year between May and June, and clutches hatch in August and September at the beginning of the rainy season, when there is greater availability of lush vegetation (2).

Although predominantly herbivorous, the Anegada ground iguana is also an opportunistic carnivore, feeding on invertebrates such as beetles, caterpillars, centipedes and roaches supplementing a diet of leaves and fruit (4). Where the iguana’s range overlaps with feral livestock, the bulk of the diet consists of plants that are rejected by the livestock. These are usually plants containing high levels of secondary compounds that are poorly digested and therefore of poor nutritional value (2).

Anegada ground iguana range

The natural range of the Anegada ground iguana has greatly reduced and is now confined to the island of Anegada in the British Virgin Islands (2). In addition two small introduced populations exist on Guana Island and Necker Island. The total population across all three islands is thought to number fewer than 200 individuals (1).

Species with a similar range

Anegada ground iguana habitat

The Anegada ground iguana is closely tied to porous limestone habitats on Anegada, with burrows of both sexes being located on old limestone reef-tract or in sandy areas next to it (4). By contrast, both Guana and Necker are largely volcanic in origin and have few naturally occurring shelter sites, so fewer burrows are used and animals are more arboreal(2).

Anegada ground iguana status

Anegada ground iguana threats

Anegada ground iguana populations have undergone a drastic decline in recent decades, leaving possibly fewer than 200 total individuals teetering on the brink of extinction (5). The drop in numbers is probably attributable to a range of threats, including habitat loss and poaching by hunters who are trafficking exotic animals (2). Most devastating, however, has been the introduction of alien species (5). Feral dogs, first reported in 1994, are known to kill adult iguanas, and predation by an exploding population of feral cats on juveniles is responsible for the deaths of many hatchlings each year (2)(5). The primary threat, however, comes from competition for food from feral livestock, with the island teeming with sheep, goats, donkeys and cattle that have been released to roam freely across Anegada (2)(4). Grazing pressure from these livestock has radically changed the composition of vegetation available to the iguana, shifting the species’ diet to rely more on plants with secondary compounds with dubious nutritional value (2).

Anegada ground iguana conservation

The Anegada Iguana Recovery Programme began in 1997, which included establishing a ‘headstart’ facility. This facility collects hatchlings and nurtures them in captivity until they can be safely released into the wild, with the aim of combating the high rates of juvenile mortality due to cat predation by raising them until they are large enough that predation will not pose as great a threat (6). The first 24 were released into the wild in October 2003, with an 84 percent survival rate, and a second group of 24 were released in October 2004, and these are currently being tracked (5). In the 1980s, small numbers of these iguanas were removed from Anegada and restored to parts of their former range, on Guana Island, where the species appears to be doing well in the absence of introduced predators (1)(2). The Guana Island Wildlife Sanctuary continues to try to rid the island of sheep, the only feral grazing competitor on the island, which may improve the habitat there for the iguanas (1). The species was also later introduced to Necker Island (2). A national park designed to protect this Critically Endangered iguana on Anegada has been approved in principle by the Anegada Lands Committee, but rampant debates over land ownership and property boundaries impede developments, and must be resolved before this project can progress (2)(4). Further conservation actions advocated include a cat eradication programme and the construction of fences around protected areas to keep livestock out. Indeed, despite the successes of the headstart programme, it is imperative that efforts are made to control livestock and to secure protected land for the survival of this species. Without prompt action, it has been suggested that these iguanas may become extinct on Anegada within the next decade (2).

Embed this ARKive thumbnail link ("portlet") by copying and pasting the code below.

Terms of Use - The displayed portlet may be used as a link from your website to ARKive's online content for private, scientific, conservation or educational purposes only. It may NOT be used within Apps.